1. Field of the Invention
The present invention relates to a CRT display device to be used in a projector apparatus etc. and is particularly suitable in reducing discharge current that flows through a CRT (cathode-ray tube) when an abnormal discharge has occurred there.
2. Description of the Related Art
In various television receivers and monitor apparatuses of the CRT type, because of the structure of the electron gun used in the CRT, an abnormal discharge may occur between the anode and the cathode (electron gun) owing to foreign matter such as dust that exists inside the CRT.
Conventionally, to prevent an abnormal discharge in the CRT, various improvements and developments have been made in the electrode shapes of the electron gun, the method for polishing the electrode surfaces, the shape of the electrode supporting glass rods, the knocking characteristic, the inside coating (employment of a coating having high peel strength), etc.
In addition to the above improvements and developments, various studies and developments have been made of the method for reducing the discharge current of an abnormal discharge to prevent the CRT itself or peripheral circuits from being damaged even if an abnormal discharge occurs inside the CRT.
An example method for reducing the discharge current when an abnormal discharge occurs inside the CRT is employment of a PCE (peak current equalizer) in which a stainless lead wire for supplying a prescribed voltage to an electrode of the electron gun is replaced by a ceramic resistor of several kilo-ohms so that the cathode-side discharge path has a relatively high impedance.
However, even if the cathode side of the CRT is given a relatively high impedance, there still remains a possibility that the cathode or the heater of the electron gun that is provided on the cathode side or a circuit part connected thereto is damaged when a relatively large discharge current flows into the cathode side.
There are other possibilities that an abnormal sound is generated inside the CRT and that the peripheral circuits operate erroneously to impair its own functions of the television receiver or the monitor apparatus.
In particular, a projector apparatus or the like in which CRTs of red (R), green (G), and blue (B) are used, when an abnormal discharge has occurred in one of the R, G, and B-CRTs, say, the R-CRT, a discharge current coming from a high-voltage capacitor that is provided in a high-voltage block for supplying an anode voltage and discharge currents caused by the coating capacitances of the other CRTs where no abnormal discharge has occurred flow into the R-CRT in an additive manner. As a result, a relatively large discharge current flows into the cathode side (electron gun) of the R-CRT where the discharge has occurred, which causes a trouble in the cathode or the heater of the electron gun or a circuit part connected thereto, for example, it is damaged.